Two-stroke internal combustion engine



Nov. 5, 194 H. R. RICARDO TWO-STROKE INTERNAL COMBUSTION ENGINE Filed NOV. 5, 1939 3 Sheets-Sheet 1 Fig. I.

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A ltomey NOV. 5, 1940. R RICARDO 2,220,661

TWO- STROKE INTERNAL COMBUSTION ENGINE I Filed Nov. 3, 1939 5 Sheets-Sheet 2 Fig. 2.

A Home y 1940- H. R. RICARDO TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Nov. 3, 1939 3 Sheets-Sheet 3 Q v D K lnvzntor 764,04

, M,I)W yxtz'm A ltorney ing piston, and there is combined with this pump Patented Nov. 5, 1940 TWO-STROKE INTERNAL COMBUSTION ENGINE Harry Ralph Ricardo, London, England Application November 3, 1939, Serial No. 302,759 In Great Britain November 2, 1938 5 Claims.

This invention relates to high speed two-stroke internal combustion engines having one or more exhaust ports in the head of the cylinder and scavenging ports in the wall of the cylinder which are uncovered by the piston therein towards the end of its out-stroke, passages through which the scavenging air flows leading to these ports from a scavenging air belt to which air is delivered by a displacer pump. This pump comprises a chamber, not necessarily a cylinder, into which the air is drawn and from which it is expelled under pressure by the positive reciprocation or oscillation of a piston member. Such a pump is therefore distinct from a rotary blower which is not employed in the improved engine.

The object of the present invention is to obviate or lessen any tendency for the exhaust gases in the working cylinder to flow back into the scavenging belt when the scavenge ports begin to be uncovered by the piston, thus allowing of a later opening of the exhaust valve or port to be used and thereby securing a greater expansion of the working fluid.

According to this invention an engine of the above type is provided with a. pump of the displacement type which delivers air through a transfer passage to the scavenging air belt, the piston member of the pump being positively driven at crankshaft speed but so out of phase with the working pistonthat the pump begins its delivery stroke at or about, and preferably shortly before the commencement of the scavenging period and ends that stroke after the scavenging ports have been closed by the worka mechanically operated valve disposed in the transfer passage between the pump andthe scavenging belt, this valve cutting off the pump and closing the transfer passage approximately at the end of the delivery stroke of the pump whereby a charge of air'under a pressure substantially above the mean pressure existent throughout the scavenging period, is trapped in the scavenging belt and in that portion .of the and the scavenging belt. Thus when the work-.

ing piston begins to uncover the scavenging ports and before the valve is opened to permit air to be delivered from the pump into the transfer passage, there is already, in this passage and the scavenge belt air under such a pressure as will sufllce to prevent or lessen any tendency for exhaust gases to flow out through the scavenging ports. The'valve which controls the delivery of air from the pump to the transfer passage is preferably of the rotary type and further it. may be convenient to construct and arrange this valve so that it,controls not only the commencement and termination of the delivery of air under pressure from the pump cylinder into the scavenging belt, but also controls the inflow of air to the pump cylinder at the commencement and termination of the suction stroke of the piston in that cylinder.

The pump may be of the type comprising a cylinder and a piston which is. reciprocated therein, or it may be of the type comprising a quadrant shaped chamber having therein-a vane functioning as a piston and oscillated about one edge. In each case as mentioned, the piston member is driven at crankshaft speed as for instance by connecting the piston member in a suitable manner to the connecting rod of the engine.

.In cases where the pump comprises a cylinder and piston reciprocated therein, the desired phasing relation between the stroke of the working piston and the stroke of the pump, may be effected by disposing the pump cylinder with its axis approximately at right angles to the axis of the working cylinder and the crankshaft axis.

The displacer pump functions in a general sense in- -a normal manner in that it supplies an air charge under pressure to the working cylinder into which this air flows through the scavenge ports. It is, however, due to the phasing relation between the working piston and its uncovering of the scavenge ports and the'movement of the piston member of the pump, combined with the timing by the valve of the delivery of air from the pump, that the object of the invention is attained. That is to say air, at a pressure substantially, above the mean pressure throughout thescavenging period, is trapped or locked up in the transfer passage and scavenge belt and this air tends to prevent back-flow of exhaust gases through the exhaust ports into the scavenge belt when these ports begin to be uncovered, even though at this moment the pump, owing to the intervention of the valve, may not have actually commenced to deliver air under pressure, or under suflicient pressure to check such back-flow. When this'timing valve establishes communication between the displacer pump and the transfer passages the pressures are such that a definite flow of scavenging air from the displacer pump into the working cylinder is assured.

Conveniently the timing valve is constructed and arranged to control not only delivery from the displacer pump into the transfer passage, but also the inflow to the pump chamber on its suction stroke in the case-where 'thedisplacer,

pump is of the reciprocating piston cylinder type.

As mentioned the valve may conveniently be ofthe rotary type, but in some cases a slide valve may be employed. In any case the valve is actuated in some convenient manner from the engine crankshaft. Some means may be provided for adjusting the timing operation of the valve but ordinarily this is not needed.

.The constructional arrangements and relations of ,the working cylinder, the displacer pump and the valve may vary in accordance with requirements.

The accompanying drawings illustrate by way of example a construction embodying the present invention which may be adopted in practice. These drawings show the invention as applied to an engine operating with compression ignition, although it is to be understood that the use of the invention is not confined to engines of that type.

Figure 1 is a sectional elevation of the improved engine showing the working cylinder, crankshaft and pump cylinder, the section being takennormal to the crankshaft axis and through the axis of the pump cylinder.

Figure 2 is a longitudinal section through the rotary valve the section being taken on the line 22 in Figure 3 looking in the direction of the arrows.

Figure 3 is a sectional end elevation showing the manner in which the rotary valve and certain accessories are driven from the crankshaft.

The two-stroke engine illustrated anddescribed herein has the following features. In the head A of the cylinder B is a combustion chamber C of the open type into which at the end of the compression stroke there is forced by the piston as much of the air charge as is practicable from the constructional point of view. In this combustion chamber is an exhaust port controlled by a poppet valve D. As will be seen the combustion chamber is conveniently situated centrallyand coaxially with the cylinder B and the exhaust port is similarly disposed centrally and coaxially in what may be regarded as the inner wall C of the combustion chamber. The inlet ports for scavenging air are formed in the wall of the cylinder B the latter being conveniently constituted by a liner inserted as shown in an outer water jacketed casing B The cylinder may, however, be formed otherwise. The inlet ports are formed as passages E through what is preferably a thickened part B of the wall of the liner B, these passages leading to the port openings on the inside of the cylinder from a scavenging air belt F which extends preferably completely around the outside of the cylinder B. The transfer passage G through which the air charge flows from the displacer pump cylinder H to the scavenging belt F is formed as shown in the wall or outer part of the crank case J. However, this transfer passage may be formed separately and arranged so as to lead to the scavenging belt F over the exterior of the crank case. 7

The displacement pump is of the cylinder and piston type and its cylinder H is conveniently formed integral with the crank case, but it may be separate therefrom and mounted on the crank case. In either case the cylinder projects from the crank case with its axis at right angles with respect to both the axis of the crankshaft K and the axis of the working cylinder B. The axis of the pump cylinder H lies in a horizontal plane situated somewhat below the horizontal plane in which lies the crankshaft axis.

The transfer passage G leads from a port H at the outer end of the displacer pump cylinder H upwards to the scavengingfbelt F. Above the pump cylinder H is a casing L which extends horizontally and contains the rotary timing valve M This casing L, like the transfer passage G,

is conveniently formed integral with a part of the crank case J. It may, however, be formed integral with the lower part of the transfer passage. In this valve casing L is formed the main air inlet L through which air is drawn into the cylinder H, this air flow to the port or ports H being controlled by the valve M.

The rotary valve M is driven in some convenient manner from the crankshaft K. The valve lies within and cooperates with a ported liner N to,control the flow of air through the port or ports H incc the cylinder H, and also the flow of air when compressed by the pump piston 0 through the port or ports H into the transfer passage G and thence through the scavenge ports E into the cylinder B.

The pump piston O is connected by a link 0 to the main connecting rod K by which the pump piston is reciprocated. Owing to the phasing relation between the movements of the working piston P and the piston 0 of the displacer pump, and the timing effected by the valve M, air under a pressure above the mean scavenging pressure is trapped in the scavenging belt F and in that portion of the transfer passage G which lies between this belt and the valve M. By rotational adjustment of the ported liner N the timing efiected by the valve, more especially the cut off of the air flow from the pump cylinder H to the transfer passage G can be varied. The ports N and N in the liner control this latter air flow while the ports, which 00- operate with ports in the casing L, control the suction inflow of air to the pump cylinder H.

The arrangement by means of which the rotary valve M is driven will be seen by reference to Figures 2 and 3. The valve M is mounted on a shaft B. so as to be rotatable therewith. On one end of this shaft R is a crank pin R which is engaged by one arm S of a cross-shaped link driven by aneccentric K on the engine crankshaft K. This link has an arm S extending laterally and oppositely to the arm S and serving to drive a dynamo and other auxiliaries as will be seen in Figure 3. An upwardly directed arm S of the link engages a crank pin on the end of the valve operating cam shaft. A downwardly directed arm S drives an oil pump situated in the sump of the engine. The crank pin R of the shaft R which carries the rotary valve also serves to drive through a drag link a water circulating pump T.

A convenient construction and arrangement for guiding the piston O of the displacer pump is shown in Figure 1. A guide rod 0 extends right through the cylinder H being fixed at itsends in the ends of the cylinder. The piston 0 slides on and is supported by this guide rod which thus not only carries theweight of the piston but sustains the angular thrust of the link 0 by means the frictional losses arising from the reciprocation of the piston O, obviates or lessens wear of guiding of the piston was effected solely by the.

cylinder.

What I claim as my invention and desire to secure by Letters Patent is:

1. In an internal combustion engine operating on the two-stroke cycle, the combination of a cylinder, a piston therein acting on a crank shaft through a connecting rod, at least one exhaust port in the cylinderhead and a poppet valve for controlling said port, ports in the cylinder wall adapted to be uncovered by the piston towards the end of its outstroke through which ports scavenging air flows from a scavenging air belt around said ports, a pump comprising a cylinder and piston reciprocating therein, said pump delivering air through a transfer passage to said air belt, means for operatively connecting the piston of the pump and the crank shaft for driving said piston from and at the same speed as the crank shaft but out of phase with the work- "ing piston so,that the pump begins its delivery stroke approximately at the commencement of the scavenging period and ends that stroke after the scavenging ports have been closed by the working piston, a rotary valve located adjacentto the pump and controlling the inlet of air to the pump during its suction stroke and also controlling the delivery of air by the pump into said transfer passage, and mechanism driven from the crank shaft for actuating said valve in such timed relationship with the operation of the pump and the main working piston that the. air flow from the pump to. the transfer passage is cut off and said passage is closed approximately at the end of the delivery stroke of the pump and thus after the closing of the scavenging ports, thereby trapping in the transfer passage and air belt air which is under a pressure substantially above the mean pressure existing throughout the scavenging period. v

2. In an internal combustion engine operating on the two-stroke cycle, the combination of a cylinder, a piston therein acting on a crank shaft through a connecting rod, at least one exhaust port in the cylinder head and a poppet valve for controlling said port, ports in the. cylinder wall adapted to be uncovered by the piston towards the end of its outstroke through which ports scavenging air flows from a scavenging air belt around said ports, a pump comprising a cylinder and piston reciprocating therein, the pump being positioned with its cylinder axis approximately at right angles to the axis of the working cylinder and to the axis to the crank shaft, said pump delivering air through a transfer passage to said air belt, a link extending from the pump piston to the connecting rod of the working piston whereby the pump is driven at the same speed as the crank shaft but out of phase with the working piston so that the pump begins its delivery stroke approximately at the commencement of the scavenging period and ends that stroke after the scavenging ports have been closed by the working piston, a rotary valve located adjacent to the pump and controlling the inlet of air to the pump during its suction stroke and also controlling the delivery of air by the pump into said transfer passage, and mechanism driven from the crank shaft for actuating said valve in such timed relationship with the operation of the pump and the main working piston that the air flow from the pump to the transfer passage is cut off and said passage is closed approximately at the end of the delivery stroke of the pump and thus eflecting the closing of the scavenging ports, thereby trapping in the transfer passage and air belt air which is under a pressure substantially above the mean pressure existing throughout the scaveng ing period.

3. In the operation, on a two-stroke cycle, of an internal combustion engine comprising a working cylinder, a piston therein adapted to drive a crank shaft, scavenging air ports in the cylinder wall adapted to be uncovered by the piston towards the end of its outstroke, a displacement pump adapted to deliver air through a passage to said ports, and a valve controlling the delivery of air from the pump to said passage; the method of controlling the scavenging of said engine which comprises prolonging the delivery stroke of the pump for a short period of time after the main piston has closed the scavenging ports, and cutting off the flow of air from the pump into said passage approximately at the end of the stroke of the pump, whereby air under pressure is trapped in said passage and will enter the cylinder scavenging ports as soon as they are uncovered during piston.

4. In the operation, on a two-stroke cycle, of an internal combustion engine comprising a working cylinder, a piston therein'adapted to drive a crank shaft, scavenging air ports in the cylinder wall adapted to be uncovered by the piston towards the end of its outstroke, a displacement pump adapted to deliver air through a passage to said ports, and a valve controlling the delivery of air from the pump to said passage; the method of controlling the scavenging of said engine which comprises beginning the delivery stroke of the pump at approximately the comthe next outstroke of the main mencement of the scavenging period, prolonging the delivery stroke of the pump for a short period of time after the main piston has closed the scavenging ports, opening the passage to flow of air 5. In the operation, on a two-stroke cycle, of

an internal combustion engine comprising a working cylinder, a piston therein adapted to drive a crank shaft, scavenging air ports in the cylinder wall adapted to be uncovered by the piston towards the end of its outstroke, a displacement pump adapted to deliver air through a passage to said ports, and a valve controlling the delivery of air from the pump to said passage; the method of controlling the scavenging of said engine which comprises beginning the delivery stroke of the pump shortly before the commencement of the scavenging period, prolonging the delivery stroke of the pump for a short period of time after the main piston has closed the scavenging ports, opening the passage to flow of air from the pump shortly after the scavenging ports begin to open, and cutting off the flow of air from the pump into said passage approximately at the end of the stroke of the pump, whereby air under pressure is trapped in said passage and will enter the cylinder scavenging ports as soon as they are uncovered during the next outstroke of the main piston.

- HARRY RALPH RICARDO. 

